The present invention relates to one-component RTV silicone rubber compositions, and more particularly the present invention relates to adhesion promoters or self-bonding additives for one-component RTV compositions.
An early type of one-component RTV composition is to be found in the disclosure of Ceyzeriat, U.S. Pat. No. 3,133,891 and Bruner, U.S. Pat. No. 3,035,016. These disclosures relate to acyloxy functional one-component compositions. In the course of time there were various inventions made of other types of RTV compositions having different functionalities; for instance, one-component ketoxime functional RTV compositions; amine functional RTV compositions; amide functional RTV compositions; aminoxy functional RTV compositions, etc.
During the course of development of such compositions, it was decided that it would be desirable for such compositions to have self-bonding additives; that is that the composition bond without a primer to various types of substrates with good adherency by the incorporation of such self-bonding additives. Examples of such self-bonding additives for such acyloxy functional RTV compositions are, for instance, to be found in disclosures of Kulpa, U.S. Pat. No. 3,296,161, Goossens, U.S. Pat. No. 3,296,195 and Beers, U.S. Pat. No. 3,438,930. The difficulty with such acyloxy functional compositions was that they were somewhat corrosive. That is, even though they were fast-curing and had other advantageous properties, they were found to be somewhat corrosive and gave off a pungent odor. Accordingly, it became desirable to develop compositions that were substantially non-corrosive and did not give off objectionable odors such that could be used in a crowded room. As stated previously, such compositions were one-component.
An example of a two-component RTV composition is, for instance, disclosed in Nitzsche et al U.S. Pat. No. 3,127,363. This patent discloses two-component compositions comprising a silanol polymer, a polysilicate cross-linking agent and preferably a tin salt of a carboxylic acid as a catalyst. While such a composition is packaged as a two-component system when it is desired to cure the composition the two components are mixed and the composition cures to a silicone elastomer. While such a composition had a sufficiently rapid curing time and was non-corrosive, nevertheless it had to be mixed prior to the use of the composition which necessitated additional labor costs. Further, the composition once it was mixed did not have an extended shelf life. An early one-component system is to be found in Nitzsche et al. U.S. Pat. No. 3,065,194 which discloses the utilization of a silanol polymer, an alkoxysilane cross-linking agent and a tin soap. While such a composition was one-component, nevertheless the composition did not have a sufficient shelf life. Further, special mixing procedures had to be utilized to prepare the composition, that is an extended drying cycle.
It was early recognized that such alkoxy functional one-component RTV systems had many advantages, and attempts were made to prepare such compositions as disclosed in Brown et al, U.S. Pat. No. 3,122,522 and Brown et al, U.S. Pat. No. 3,161,614, or U.S. Pat. No. RE-29760. However, these compositions did not have a sufficiently fast cure rate and had very poor shelf stability. Other alkoxy functional RTV compositions, for instance are to be found in Weyenberg U.S. Pat. No. 3,334,067, Cooper et al, U.S. Pat. No. 3,542,901, Smith et al, U.S. Pat. Nos. 3,689,454 and 3,779,986. These latter patents and specifically the Weyenberg and the Smith patent utilize specialized titanium chelate catalysts as condensation catalysts for such alkoxy functional one-component RTV compositions. Such titanium chelate catalysts were desirable in that they imparted to the alkoxy functional RTV a commercial cure rate; that is, the cure rate was such that the composition could be commercialized. However, the composition was still not a fast-curing one-component RTV system.
Another attempt to make such composition fast-curing and also have desirable shelf stability properties and self-bonding properties is to be found in the disclosure of Beers, U.S. Pat. No. 4,100,129. However, such composition still was not as fast-curing and still did not have as good a shelf stability as would be desirable.
It has been theorized recently that such earlier compositions suffered from the fact that there was excess methanol, silanol or hydroxy groups in the polymer system after it had been prepared even though it was prepared in the substantial absence of moisture. Such hydroxy groups in the polymer system resulted in the premature cross-linking of the polymers such that there resulted a poorly curing composition, that is one that did not have a sufficient cure rate and a good shelf stability. Accordingly, a system was devised in which there could be utilized a scavenger in the composition to react with excess hydroxy groups whether from methanol, silanol, or water, and would not react with the alkoxy groups to prematurely cross-link the RTV system. The disclosure of how this is accomplished as well as the scavenging systems for such a composition is for instance disclosed in the patent of White et al, U.S. Pat. No. 4,395,526 and in the patent of John B. Halgren, U.S. Pat. No. 4,377,706. The compositions of White, et al while sufficiently fast-curing and having shelf stability, nevertheless, had to be modified to meet certain requirements; that is, such compositions did not bond to most substrates. In the absence of a primer such compositions have very little or no self-bonding properties. Accordingly, it became highly desirable to develop self-bonding additives for such compositions. It should be noted that in addition to the self-bonding additives disclosed before, there are other patents on useful self-bonding additives for both two-component and one-component RTV systems. (RTV in this application refers to room temperature vulcanizable.) For instance, note Bessemer et al, U.S. Pat. No. 3,888,815 which relates to self-bonding additives for two-component RTV systems in which the functionality of the self-bonding additives, which in addition to alkoxy, may be selected from amino, carbonyl, carboxy, isocyano, azo, diazo, thio, thia, dithia, isothiocyano, oxo, oxa, halo, ester, nitrose, sulfhydryl, hydrocarbonylamido, sulfonamido and combinations thereof. Also note the disclosure of Smith, U.S. Pat. No. 4,147,685 which relates to primer compositions and specifically the acrylate functional silanes of that patent which may be utilized as self-bonding additives for RTV compositions and disclosed in the patent application of Keating, Ser. No. 109,727, filed on Jan. 4, 1980.
Other disclosures on self-bonding additives for RTV systems for instance are to be found in Beers, U.S. Pat. No. 4,100,129 which was referred to previously and Mitchell et al, U.S. Pat. No. 4,273,698. The Mitchell et al patent discloses various silyl fumarates, succinates, and maleates which can be utilized as self-bonding additives in one-component RTV systems. However, none of these patents which are all incorporated by reference in the present case, disclose self-bonding additives for the compositions of White et al, U.S. Pat. No. 4,395,526. A self-bonding additive is desirable, otherwise there has to be utilized a primer. The use of a primer involves added labor costs which are considerably more than the additional cost of a self-bonding additive when it is incorporated into the composition during the manufacture of the composition. Accordingly, it is highly desirable to have a self-bonding additive or additives in the compositions of White et al, U.S. Pat. No. 4,395,526.
It is one object of the present invention to provide for adhesion promoters or self-bonding additives for one-component alkoxy functional RTV compositions.
It is an additional object of the present invention to provide self-bonding additives for alkoxy functional, one-component RTV systems which self-bonding additives will give self-bonding properties to the RTV compositions and to most substrates.
It is yet an additional object of the present invention to provide adhesion promoters or self-bonding additives to alkoxy-functional one-component RTV systems which have a fast cure rate and are shelf stable and which self-bonding additives will affect the physical properties and the curing properties of the RTV system.
It is a further object of the present invention to provide a process for producing a self-bonding one-component alkoxy-functional RTV system which has a fast cure rate, and is shelf stable by incorporating in the RTV system self-bonding additives.
These and other objects of the present invention are accomplished by means of the disclosures set forth herein below.